riscv: Clean up IPI initialization code

The previous IPI code initialized the device whenever the first call was
made to a riscv_*_ipi function. This made it difficult to determine when
the IPI device was initialized. This patch introduces a new function
riscv_init_ipi. It is called once during arch_cpu_init_dm. In SPL, it is
called in spl_invoke_opensbi. Before this point, no riscv_*_ipi functions
should be called.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>

common/spl/spl_opensbi.c

@@ -79,6 +79,11 @@ void spl_invoke_opensbi(struct spl_image_info *spl_image)
 	invalidate_icache_all();
 
 #ifdef CONFIG_SPL_SMP
+	/* Initialize the IPI before we use it */
+	ret = riscv_init_ipi();
+	if (ret)
+		hang();
+
 	/*
 	 * Start OpenSBI on all secondary harts and wait for acknowledgment.
 	 *